Folded line oscillator



Sept. 21, 1954 H, M BROWN 2,689,915

F OLDED LINE OSCILLATOR Syvum/vm HUGH M. BROWN @www Patented Sept. 21, 1954 FOLDED LINE OSCILLATOR Application November 4, 1944, Serial No. 561,943

UNITED STATES PATENT OFFICE Claims.

This invention relates to an oscillator capable of producing electrical oscillations in the ultra high frequency band, particularly intermittent or pulsed oscillations.

Previous oscillators have often been found to 5 be unsuitable for pulsed operation because of failure to commence oscillating immediately upon being energized. Furthermore, previous oscillators of the type employing a coaxial transmission line or a cavity in the anode-grid circuit of the oscillator tube are often characterized by excessive physical length of the line or cavity. In addition, adequate means for feeding back energy of proper amount and phase between the output and excitation circuits of the oscillator have often been diicult to attain. And finally, the problem of providing a suitable connector for the anode terminal of the oscillator tube which will provide good electrical contact and at the same time conduct away the heat generated at the anode has often been a difcult one.

Accordingly, it is an object of this invention `gto produce an oscillator capable of being satisi'factorily pulsed into intermittent oscillation. It gi s a further object of this invention to create an25 scillator which will start oscillating immediately pon being energized, and which may be use to produce satisfactorily either pulsed or con Y $5 y tinuous oscillations.

A further object of this invention is to produce an oscillator having a shortened physical length of the anode-grid resonant line while retaining the necessary electrical length of line.

An additional object of this invention is to produce oscillator resonant circuits having therebetween an effective type of feedback for transferring energy from one circuit to the other to sustain oscillations.

A still further object is to produce novel means for providing good electrical contact to the anode terminal of the oscillator tube, and also to provide a contact which will readily conduct heat away from the anode.

With these objects in mind, an exemplary embodiment of this oscillator is shown in the drawings in which,

Figure 1 shows a sectionalized elevation of the oscillator taken along lines I-I of Figures 2 and 3.

Figure 2 shows a cross-section of the oscillator taken along line 2 2 of Figure 1,

Figure 3 shows a cross-sectional view illustrating the diaphragm between oscillator resonant circuits and taken along line 3-3 of Figure l,

Figure 4 shows a schematic diagram of the os- (Cl. Z50- 36) 2 cillator illustrating the auxiliary circuit completing the electrical features of the oscillator,

Figure 5 illustrates the equivalent circuit of the oscillator,

Figure 6 is enlarged view showing one element of the anode connector illustrated also in Figure l,

Figure '7 is a schematic view of another embodiment of this invention and,

Figure 8 is a schematic view of an additional embodiment of this invention.

Figure 1 illustrates the preferred embodiment of the oscillator, which is shown schematically in Figure 4. The outer body I0 of the oscillator is shown consisting of a part II, and a part I2, forming together a single conducting cylinder. Parts Il and I2 are divided within the oscillator by a transverse diaphragm I3, completely separating parts II and I2 of the body Ill except for a hole in the center through which electron tube Ill extends. In addition, arcuate slots I5 shown in Figure 3, are cut in diaphragm I3 near the central hole through which tube I4 extends.

Tube I4, which is held inside oscillator body I0 by inner cylinder IB, is a conventional type of triode known as a lighthouse tube. The cathode of the tube is directly connected to one of the tube prongs shown. In addition, an annular capacitor, built into the tube, connects the cathode of the tube with the lower shell 20 of the tube. Thus, insofar as radial frequency energy is concerned, the cathode of tube lli may be regarded as being connected directly to the lower shell 20, which in turn contacts rmly the inner surface of cylinder I6.

The control electrode or grid of lighthouse tube I 4 is connected to external conducting annular member 2| which forms part of the tube and which, as shown in Figure l, is wedged into good conducting relation with ring Z2 anchored at its edge to the central hole in diaphragm I3. The grid of tube I4 is thus connected through ring 22 to diaphragm I3, which is in turn anchored around its edge to outer body I0. Coaxial cylinders II and I6 thus constitute a coaxial transmission line connecting at one end shell 2D, connected to the cathode, and at the other end diaphragm I3, connected to the grid. The coaxial line thus formed is short circuited at the extremity of body I0 by the annular closure member 23. The electrical length of the transmission line formed by the cooperation of cylinders I I and I6 may be made approximately equal to a quarter wave length of the desired frequency of oscillation by properly selecting the axial length of the cavity formed between diaphragm I3 and annular closure member 23. When properly adjusted, a circuit slightly capacitive at the midband point of the desired frequency band of oscillation is created between the cathode and grid of tube I4, as shown schematically at 24 in Figure 5.

A resonant circuit 25 (Figure 5) is also connected between the grid and anode of tube I4. AS seen in Figure 1, part |2 of body I0 constittues the outer conductor of a second transmission line. The inner conductor of this transmission line is formed by cylinder 26 anchored to connector 34, which in turn bears against anode terminal 33. The inner surface of cylinder |2 and the outer surface of cylinder 26 cooperate to form a coaxial transmission line extending away from diaphragm |3. Cylinder I2 is partially closed at its end by annular closure member 30 through the center of which penetrates a smaller cylinder 3| into the body of the oscillator, extending to within cylinder 26. Annular member 30 and cylinder 3| thus constitute a folded extension of outer conductor I2 of the transmission line |2-26. The electric field of the transmission line thus extends away from diaphragm I3 along the annular chamber between cylinders I2 and 26, reaches annular member 36 at the end of the oscillator, and is doubled back into itself, using the outer surface of cylinder 3| and the inner surface of cylinder 26, as a folded extension of the line.

There is thus formed a coaxial transmission line doubled inwardly back into itself to maintain a given electrical length while shortening the actua1 physical length by approximately the axial distance that cylinder 3| penetrates into cylinder 26.

In the preferred embodiment of this invention illustrated in Figure 1, a second fold is made in the line by the use of internal cylinder 32 which, like cylinder 26, is also anchored to connector 34. Tube terminal 33 makes good electrical and thermal contact with the special anode connector 34 to be particularly described hereinafter. The inclusion of cylinder 32 extends electrically the line which would otherwise terminate at 35. The line formed by the cooperation of the outer surface of cylinder 3| and the inner surface of cylinder 26 continues around through annular member 36, along connector 34, and to the outside surface of cylinder 32 and the inside surface of cylinder 3|. The line finally terminates, open circuited, in the region designated 46. As mentioned before, the line just described is shown schematically at 25 in Figure 5.

The end of cylinder 32 is closed by a rounded cap 4| which eliminates sharp corners on conducting surfaces, thereby preventing arc-over between cylinders 32 and 3|.

Feed-back energy necessary to sustain oscillations is transferred between cathode-grid resonant line 24 and anode-grid resonant line 25 described above, by the action of feedback probes 42, anchored at their bases to cylinder I6. The action of the feedback probes 42 has been symbolized in schematic diagram Figure as a condenser 43 connected between cathode and anode of tube I4. While experiments to date indicate that this is the principal action provided by the probes 42, there is considerable evidence to indicate that the reaction between probes 42 and grid diaphragm I3 also has an appreciable effect on the feedback between resonant circuits 24 and 25 (Figure 5).

In order to minimize the danger of arc-over 355i etween surfaces within the oscillator body, all ,gedges are rounded as shown, for example, in the As illustrated in Figure 1, cylinder 26, which is anchored xedly to member 36, connector 34 and cylinder 32, is held in place within the body of larger cylinder I2 by three insulating holders 44, one of which is shown in Figure 1. Insulating holders 44 are placed between cylinder 26 and annular member 3|) at the position of a voltage node or minimum, thereby minimizing the danger from spark-over at the insulating support. Tracing the standing wave on the anode-grid transmission line, which is an electrical half wave length long, it will be seen that a voltage loop or maximum appears between annular member 36 and diaphragm I3. Proceeding along the line between cylinders I2 and 26 away from diaphragm I3, the voltage decreases until a voltage node or minimum is reached in the region of the insulator 44. The voltage then increases in opposite phase between cylinders 26 and 3| and between cylinders 3| and 32, reaching a maximum at the open end of the line at 40, between cylinders 3| and 32. It will thus be seen that the minimum voltage, and hence the optimum point for placement of the insulating holder 44, is approximately as shown in Figure 1. This region also is the region of a current anti-node or maximum, and for this reason output from the oscillator is taken by loop coupling from the vicinity of insulating member 44. This loop 45 is connected to the inside of transmission line cylinder I2 at 46, bending around to form the inner conductor of the outp-ut coaxial transmission line, the outer conductor of which is shown at 50.

ring shaped termination 5| of probes 42, and in the rounded cap 4| which closes cylinder 32.

Anode connector 34 will now be more particularly described by reference to Figures 1 and 6. Connector 34 may be best described as a series of three nested thimbles, most clearly seen in Figure l. A hole is made in the end of the thimbles into which anode terminal 33 may be inserted. A plurality of axial, diametrical slots 52 are cut in the end of the thimbles almost down to the base 53, as shown in Figure 6, which illustrates, in the interest of clarity, only the outer of the three nested thimbles. Slots 52 result in a series of fingers 54 extending away from the base or ring 53 in a direction parallel to the axis thereof, and bending sharply in toward the axis of the ring, where they contact the anode terminal 33 (Figure 1). The larger thimble, being on the outside, has comparatively long radial fingers, while the inner thimble has short radial fingers becaue of its position closer to the axis of the thimble and hence closer to anode terminal 33. The resulting connector makes good electrical and thermal contact with anode terminal 33, and in addition permits considerable rocking and lateral motion of terminal 33 within the hole in connector 34 while retaining good conductive relationship therewith.

The oscillator described above is made tunable by providing means for allowing cylinder 3| to slide axially within annular member 30. Pulling out cylinder 3| shortens the effective length of the grid-anode resonant transmission line thereby increasing the frequency of oscillation. It will be noted that axial movement of cylinder 3| affects not only the portion of the line between cylinders 26 and 3| but also that portion o1 the line between cylinders 3| and 32. Movement of cylinder 3| thus has twice the effect it the action of wing nuts 6| screwed on to bolts 5 would have if the line had only a single fold, as in the embodiment shown schematically in Figure '1. It has been found in practice that the electrical length of the cathode-grid line of the oscillator has little eiect on oscillator operation; in fact this line may be even completely omitted, if desired or, if desired this line may be made tunable as shown in Figure 7. In the preferred embodiment illustrated in Figure 1, the annular member 23 is fixed in the body l0 in such a position that the line is slightly capacitive at the mid-band frequency, without serious detriment to the tunable feature of this oscillator.

Anode supply voltage is introduced into the oscillator through a chimney 51 which holds a conducting cylinder 58. Voltage is applied to cylinder 26 by conductor 59 terminated in a quarter-wave choke in the form of spring 55. A bypass condenser to prevent any RF which might leak through choke 55 from reaching the B| source is provided in the form of an annular dielectric member 56 inserted between conductor 59 and cylinder 58.

/Tube I4 is held firmly in place in cylinder I6 by a cylinder 60 which presses base 2Q into the body of the oscillator and causes annular grid ring 2| to bear firmly against ring 22. Cylinder 6D is held within body I0 of the oscillator by,

Referring to Figure 4, the auxiliary electrica ircuit used in connection with the oscillator wi ow be described. A pulse transformer 64 pro uces a short pulse of high voltage between th cathode and the anode of the oscillator tube caus ng the oscillator to break into immediate oscilla ion. Resistors 65 and 66 are placed in th roduce the proper biases for optimum operatic f the oscillator. As shown, the outside cylin der l0 of the oscillator is grounded, thereby sim plifying the problem of installation in the chass of radio apparatus.

Figure 1 illustrates schematically an embodiment of this invention using only a single fold in the anode-grid line instead of a double fold. As will be seen, this is accomplished by omitting cylinder 32 from the anode portion of the transmission line and altering slightly the relative dimensions of the parts. As with the double fold, the single folded embodiment of Figure '7 may be tuned by axial movement of cylinder 3l.

Figure 8 illustrates an embodiment of this invention in which the transmission line is folded outwardly instead of inwardly. Referring to Figure 8, the transmission line starts at grid cylinder and the anode cylinder 1I, proceeds axially away from the grid diaphragm to the end of the chamber where it folds back and outward and then proceeds along cylinder 1B and cylinder 12. It then refolds outward again, proceeding along cylinder 13 and cylinder 12 and is terminated in a short circuit at wall 14. Inasmuch as the transmission line in the embodiment shown in Figure 8 is short circuited at its end, this oscillator will operate in a mode corresponding to an odd quarter-wave length; that is, one quarter-wave length or three quarter-wave lengths, for example, instead of as a half-wave length line as in the open-circuited embodiment illustrated in Figure 1. Any of the embodiments shown in Figures 4, 7, and 8 may be tuned, if desired, by use of an axially slidable annular member shown, for example, in the schematic diagram, Figure 8, at 15. Annular member may be either of conducting or non-conducting maathode and grid lines respectively, as shown, t

6"v terial and may be moved thru a finger 16 extending thru the cylinder 13 or thru a rod inserted thru a hole in wall 14.

I claim:

l. In a multi-electrode vacuum tube cavity oscillator, an oscillator cavity comprising a cylinder forming the inner conductor of a coaxial transmission line and adapted to be connected at one end to one electrode of the oscillator tube, and a second cylinder forming the outer conductor of said line and adapted to be connected at one end to another` electrode of the tube, one of said cylinders extending axially beyond said other cylinder and being doubled back around the end of said other cylinder to form a fold in said line.

2. In a vacuum tube cavity oscillator for an oscillator tube having anode and control electrode terminals, an oscillator cavity comprising a rst cylinder adapted to be connected to the control electrode terminal of the oscillator tube, a second cylinder located within said first cylinder and having the end nearest the connection of the control electrode to the first cylinder adapted to be connected to the anode terminal of the tube, and a third cylinder located partially within and extending outside the other end of said second cylinder and connected to said first cylinder at a point remote from the control electrode connection thereto.

3. In a cavity oscillator for an oscillator tube having coaxial anode, cathode, and control grid terminals, a rst cylinder adapted to be connected at one end to the control grid terminal, a second cylinder located within said first cylinder and having a reentrant flange at one end connected to the anode terminal, a third cylinder located partially within and extending outside of said second cylinder and connected to the other end of said first cylinder, and a fourth cylinder connected to said anode terminal and located Within said second cylinder and extending partially within said third cylinder.

4. In a cavity oscillator for an oscillator tube having coaxial anode, cathode, and control grid terminals, a rst cavity comprising an inner cylinder connected to the cathode terminal and an outer cylinder connected to the grid terminal, an apertured circular plate forming the connection between said grid terminal and said outer cylinder, a second cavity comprising a first cylinder connected at one end to said circular plate, a second cylinder located within said first cylinder and adapted to be connected at one end to the anode terminal of the tube, a third cylinder` located partially within and extending outside of said second cylinder and connected to the other end of said first cylinder, and feedback means extending through the apertures in said plate to couple said first and second cavities.

5. In a cavity oscillator for an oscillator tube having coaxial anode, cathode, and control grid terminals, a rst cavity comprising an inner cylinder connected to the cathode terminal and an outer cylinder connected to the grid terminal, an apertured circular plate forming the connection between said grid terminal and said outer cylinder, a second cavity comprising a first cylinder connected at one end to said circular plate, a second cylinder located within said first cylinder and having a reentrant flange at one end connected to the anode terminal, a third cylinder located partially within and extending outside of said second cylinder and connected to the other end of said first cylinder, a fourth cylinder References Cited in the le of this patent UNITED STATES PATENTS Number Name Date MacDonald Apr. 24, 1928 Potter Feb. 8, 1938 Linde Oct. 17, 1939 Lindenblad Dec. 5, 1939 Number 8 Name Date Hansen Feb. 20, 1940 Wolff July 16, 1940 McArthur May 26, 1942 Chevigny June 20, 1944 Allerding June 20, 1944 Beggs Feb. 25, 1947 Llewellyn Aug. 19, 1947 Jensen Sept. 16, 1947 Hansen Apr. 6, 1948 Gurewitch July 19, 1949 Kuper Sept. 19, 1950 

